Variation in sister chromatid exchange frequencies between human and pig whole blood, plasma leukocyte, and mononuclear leukocyte cultures.

Sister chromatid exchange (SCE) induction by ultraviolet (UV) light was studied in both human and pig whole blood cultures (WBC) and plasma leukocyte cultures (PLC). No variation in SCE frequency was observed between pig WBC and PLC in control as well as in treated cells. Conversely, SCE frequencies of human PLC were consistently higher than those of WBC in control and UV-exposed cells. Thus, red blood cells (RBCs) do not influence the sensitivity of lymphocytes to UV light exposure, and there must be some different culture condition(s) in the induction of SCEs between human WBC and PLC but not in swine lymphocyte cultures. Since the BrdUrd/lymphocyte ratio of WBC was halved in PLC, the effect of BrdUrd concentration in inducing the SCE baseline frequency of PLC may be ruled out. Also, Ficoll-Hypaque-separated human mononuclear leukocytes in culture (MLC), but not pig MLC, showed a two-fold increase in SCE frequency over WBC values. Thus, neither the cell separation technique nor polymorphonuclear leukocytes had a significant role in the elevated SCE frequency of human PLC or MLC. Experiments where human RBCs were titrated into human PLC showed that the induction of an elevated SCE frequency of PLC was suppressed in a dose-dependent manner by the presence of RBCs in the culture medium. Since the incorporation of pig or human RBCs into human PLC as well as into MLC reduced the SCE frequency to that of WBC, a common component and/or function existing in these cells is suggested. Analysis of different RBC components showed that RBCs, specifically RBC ghosts, release a diffusible but not dialyzable "corrective" factor into culture medium that is able to reduce the SCE frequencies of PLC. Antioxidant enzymes such as catalase and horseradish peroxidase were unable to reduce the SCE frequency of human PLC to WBC values.